The broad, long-term objectives of this proposal are to establish a foundation for independent research in human neurophysiology, with focus on cognitive processes during normal and abnormal states of consciousness. The research component of this proposal will center on investigation of the persistent vegetative state (PVS). PVS is a tragic "experiment of nature" in which behavioral state changes superficially resembling sleep- wake cycles occur, but the wakefulness is without apparent cognitive awareness. The research is designed to address the following fundamental issues: 1. Does cognitive processing occur in PVS?, and 2. What are the similarities and differences between normal sleep-wake cycles and the state changes that occur in PVS? The experimental design and methods to be used are: 1. A series of evoked responses to assess cognition in these patients, including assessing the ability to recognize novelty, the ability to extract meaning from words, and the ability to recognize a personally meaningful stimulus; and 2. Behavioral, electroencephalographic, and polygraphic studies to assess state changes and their relationship to normal sleep-wake cycles. Study of patients in PVS provides a unique opportunity to study fragments of the normal behavioral and cognitive repertoire, to gain insight into the steps involved in normal cognitive processing, and to correlate these functions with anatomy. When research achieves the expected goals, we will be in a better position to judge prognosis and assess possible therapeutic options in these patients.